Method of and means for preventing condensation of moisture from flue gases



Aug. 26, 1930.

s s. SCHMIDT 1 1,773,870 METHOD OF AND MEANS FOR PREVENTING CONDENSATION 0 F MOIS-TURE FROM 'FLUE GASES Filed April 3, 1928 WVZW 70/? ATTOR/VKYJ.

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Patented Aug. 26, 1930 UNITED STATES PATIENT OFFICE GEORGE G. SCHMIDT, OF FOREST HILLS, NEW YORK, ASSIGNOR TO CARRIER ENGINEER- ING CORPORATION, OF NEWARK, NEW JERSEY METHOD OF AND MEANS FOR- PREVENTING OONDENSATION OF MOISTURE FROM FLUE GASES Application filed April 3, 1928. Serial No. 267,094.

In some furnaces, particularly air heating furnaces 1n wh1ch gaseous and other hydrocarbon fuels are burned for heating the air, there isconsiderable condensation of moisture from the water vapor in the products of combustion and flue gases if the heat transfer from the hot gases to the air is such as to give good heating efliciency. The condensate not only corrodes and destroys the metal parts of the furnace with which it comes in contact, p

but it also is injurious to the metal, mortar and brick of the smoke flues or chimneys and is otherwise objectionable. The efficiency of the furnace is increased if the design is such that the exchange of heat from the gases of combustion to the air being heated is sufficient to cool the ases to or below their point of saturation, ut the resulting condensation from the gases is a source of serious objection and much trouble, as before indicated.

The object of my invention is to prevent condensation from the flue gases in the smoke flue or other flues or parts with which the gases come in contact and where such a result desideratum. This object is accomplished by the introduction into the flue gases or products of combustion of air having such condition as to its temperature or moisture content,

' or both, that the mixtureof the air and gases will be unsaturated and will have a lower dew point or a greater moisture-carrying ca pacitythan the flue gases before the admixture of the air, thereby preventing the condensation which would otherwise take place.

The accompanying drawings illustrate an air heating furnace equipped with means embodying my invention for preventing condensation from the flue gases.

Fig. 1 is a vertical, longitudinal, sectional elevation of the furnace.

Fig. 2 is a transverse,'sectional'elevation of the same through the air heating unit or heat interchanger.

My invention is applicable to furnaces of I different constructions, and the construction illustrated in .-the drawings and hereinafter described'lis selectedsimply to give a clear understanding of a practical application of the invention. 7

- In said furnace, which is provided with an air heating or heat interchange unit having separate or non-communicating flues or passages'through which the gases of combustion and air respectively pass in heat interchange relation to each other so that the hot gases heat the air, 10 represents the furnace casing, 11 the air heating unit and12' the fire box or combustion chamber in which the combustion of the fuel from one or more burners 13 takes ace.

The air heating unit 11 shown, is provided with vertical air flues or passages 14 through which the air to be heated passes, and with substantially horizontal gas flues or passages 15 through which the gases of combustion or flue gases pass on their way from the combustion chamber to the smoke flue. The air passages l f communicate at their upper and lower ends with the air space in the furnace casing '10, and alternate with the gas passages 15 which communicate at opposite ends with headers 16 and 17. The gases pass from the combustion chamber 12 through one or more suitable openings or passages 18 into the inlet header 16, and pass from the latter through the gas passages 15 of the heat interchanger to the discharge header 1-7 which communicates with the smoke flue 19. The hot gases or products of combustion passing through the flues 15 of the interchanger heat the air passing upwardly through the air passages 14 of the heat interchanger. The combustion chamber 12 and inlet header 16 are shown as being spaced from the walls of the casing 10 so that a portion of theair can pass over or around the combustion chamber and the head er 16 and be heated by these parts, which are the hottest parts of the furnace.

A suitable-fan 20 is shown having its air discharge connected with the air space in the lower portion of the furnace casing for forcing the air under pressure through the air space and changer and through one or more hot air dischargeaflues 21 by whicg the heated air-is delivered tolthe desired ,nt or ppints.

If the furnace is designed tOjg Ve maxithe air'pass ages of the-"heat inter- 7 mum heating efficiency, the gases of combustion will be cooled below their point of saturation in the heat interchanger, and there will be a substantial condensation of moisture, which, of course, increases its efficiency. It, therefore, follows that the flue gases or prod acts of combustion leaving the furnaceor heat interchanger will be saturated or so near the saturation point as to cause condensation in the smoke flue or connections between the same and the furnace, with the recognized objectionable results and injurious attack on the parts with which the condensate comes into contact.

A simple and efficient means for preventing such condensation of moisture from the flue gases leaving the furnace consists of an air pipe, tube or passage 25 arranged so as to receive hot air which has been heated by the furnace and deliver the same into the flue gases. As shown in the drawings, the pipe 25 may be arranged in the hot air space in the furnace casing above the air heating unit 11 with the inlet end 26 of the pipe extending down to a point adjacent the combustion chamber 12, or the inlet header 16 of the air heating unit, and the discharge end 27 of the pipe extending into the smoke flue. By this arrangement, the hottest air from the furnace, which is that adjacent the walls of the combustion chamber 12 and the inlet header 16, is delivered by the air pipe 25 into the smoke flue.

The pipe 25 is of small size. as only a small quantity of this hot air, which is of higher temperature than the flue gases, is sufficient to prevent the condensation in the flue gases, and the Waste of the heated air is not great enough to be objectionable. The pipe 25 could be arranged to take their from any part of the furnace where the temperature of the air is high enough. Since theair fan 20 creates a pressure somewhat above atmospheric pressure within the furnace casing 10,

the hot air will be forced under pressure through the pipe 25 into the smoke fine, and if the discharge endof the air pipe 25 is disposed in the smoke flue above the usual back draft opening 28 of the smoke flue. as shown in the drawings; it will act as an ejector and insure an active mixture of the hot air with the flue gases, as well as increasing the draft a of the flue.

(ill

tively low dew point.

taken from the building which is being heated, or from out of doors, is heated by the gases and assists somewhat rather than preventing condensation in the flue.

While in the construction shown in the drawings, the hot air is introduced into the smoke flue, manifestly it could be introduced into other parts where it maybe desired to prevent condensation from the gases of combustion after they have served their heating function. Furthermore, while in an air heating furnace, the furnace-heated air is the preferred medium for introduction into the flue gases, it is obvious that some other suitable gas could be used instead of air.

I claim as my invention:

1. The method of preventing condensation from the flue gases of furnaces which consists in the introduction into the flue gases afterthe combustion thereof of a relatively small amount of a medium having a temperature and a moisture content such as to produce an unsaturated mixture of the air and flue gases.

2. The method of preventing condensation from the flue gases of furnaces which con sists in the introduction into the flue gases after the combustion thereof of a relatively small amount of a medium having a temperature and a moisture content such as to produce an unsaturated mixture of the air and flue gases, and under a pressure above that of the atmosphere.

3. The method of preventing condensation fromthe flue gases of furnaces which consists in the introduction'into the flue gases after-the combustion thereof of a medium which has been heated by the furnace to a temperature to produce anunsaturated mixture of the air and flue gases.

4. The method of preventing condensation from the flue gases of furnaces which consists in the lntroduetlon into the flue gases of a medium wlnch has been heated by the furnace ,and has a temperature higher than the temperature of the flue ases at the point where the air is introduced into the flue gases and under aa-pressure above that of the atmosphere. v

I 5. The method of preventing condensation from the flue'gases of furnaces which consists in the introduction into the flue gases after the combustion thereof of a relatively small volume of air having a condition such as to produce an unsaturated mixture of the air and flue gases.

6. The combination of a furnace having means for heating a ir',a' flue through which the flue gases of thefurnace pass after being utilized to heat said air and which leads to an exit separate from the exit for the heated air, and means for-introducing a portion of the heated air from said air heating means into 'said flue to mix with said flue gases.

7. The combination of a furnace constructed with means for heatlng a1r, a flue for the passage of the flue gasesof the fur-v nace, said furnace having an exit for the heated air separate from the exit for the flue gases, an air forcing device, and a passage through which said forcing device delivers a portion of the air under pressure from said I an heating means into said flue to mix with said flue gases:

8. In an air heating furnace constructed with separate passagesforv the air and for ethe combustion gases arranged in heat exchange relation and having separate exits for the discharge from the furnace of the heated air and the gases of combustion,, means for the introduction into the combustion gases of a small amount of-the air which has been heated by the combustion gases for preventing condensation from the combustion gases.

9. In an air heating furnace having separate passages for the air and for the combustion gases with separate exits for the discharge from the furnace of the heated air and the gases of combustion, and a relatively small passage arranged to receive air which has been heated by the furnace, and deliver the same into the combustion gases for preventing condensation from the latter.

10. In an air heating furnace having separate passages for the-air and for the combustion gases with separate exits for the discharge from the furnace of the heated air and the gases of combustion, and a relatively small passage arranged to receive air which has been heated by the furnace, and means for delivering .the air under pressure through .said small passage into the combustion gases to prevent condensation from the latter.

11. In a heater, the combination with a hydrocarbon fuel burner and a chimney flue for the discharge of gases of combustion, of means for discharging into said flue agaseous medium having a relative humidity lower than that of said gases of combustion and in a quantity suflicient to prevent condensation in said flue from the gases of combustion.

12. In a heater of the ty e having a hydrocarbon fuel burner and a cflimnev flue for the discharge of gases of combustion from said burner, means for collecting hot air from said heater and discharging it into said flue in a quantity sufficient to. prevent condensation therein from said gases of combustion.

13. In a heater of theZt-ype delivering a current of warm" air and having a h drocarbon fuel burner and a chimney flue v or the dis charge of gases of combustion from' said burner, a pipe for receiving hot air from said heater and discharging it.into said flue for mixture with said gases and ma quantlty sufficient to prevent condensation therein,

' from said gases of combustion.

14. In a heater of the type delivering a current of warm; air and having a burner and a chimney flue for discharging the prodnets of combustion from said burner, a pipe for receiving hot air from the hottest section of the heater and discharging it into said flue with said gases, in a quantity sufficient to prevent condensation in said flue of any moisture in said gases.

15. In a heater, a burner, a heat exchange unit, a chimney flue'for the products of combustion from said burner, an, air chamber around said unit, a blower for forcing air through said chamber to be heated thereby, a pipe for collecting air heated in said chainber and discharging it under the air pressure of said chamber into said flue to facilitate the discharge of said products and prevent condensation in said flue from said around said unit, a blower for forcing air through said chamber to be heated thereby, a pipe for collecting air heated in said chamber and discharging it under the air pressure of said chamber into said flue and in the direc tion of flow of said gases in said flue tov facilitate the discharge of said products and prevent condensation in said flue from said products.

18. In a'heater, a burner, a chimney'flue ,for thedischarge of gases of combustion from said burner, said flue having therein a back draft opening, and means for discharging into said flue, in the direction of normal flow of said gases'therein, a jet ofa gaseous me- .dium with a temperature and humidity and in a quantity such that when mixed with said gases, it will prevent condensation in said flue, and will aid the normal movement of gases through said flue.

19. In a heater, a burner, a chimney flue for the discharge of gases of combustion from said burner,fsaid flue having a back draft opening, and cans for delivering a jet of hot air from sai heater into said flue for mixture with said gases and with air enter,- ing through said back draft opening to prevent condensation in said flue and to assist in the normal movement of said gases through said flue.

20. In a heater, a burner, a heat exchange unit connected to said burner, a chimney flue connected to said unit and having therein a back draft opening for discharging the gases of combustion from said burner and unit, an air chamber around said unit, a blower for forcing air through said chamber to be heated thereby, a pipe for collecting a quantity of air heated in said chamber and discharging it under the air pressure of said chamber into said flue to assist the movement of said gases through said flue and to prevent condensation in said flue from said gases.

21. In a heater, :1 burner, a chimney flue for discharging the gases of combustion from said burner, said flue including two sections, the outer of sand sections having a flared endsurrounding the adjacent end of the inner section to provide a back draft opening facing rearwardly of the normal direction of flow of gases through said flue, and means for discharging into the flared end of said out-er section, and in the direction of normal flo'w of said gases therethrough', a jet of agaseous medium having such a temperature and relative humidity and in such quantity that condensation in said outer flue section will be prevented, and the movement of said gases therethrough will be assisted.

22. In a heater, a burner, a heat exchange unit, a chimney flue for discharging the gases of combustion from said burner, an air chamher around said unit, 'a blower for forcing air through said chamber to be heated thereby, said flue comprising two sections arranged endwise of one another, the inner end i of the outer section being flared over the outer end-of the inner section'to provide a back draft openingjareund the outer end of the inner section, a baifle in said flared end to prevent back draft from the outer section into the inner section, a pipe for receiving some of theair heated in said chamber and discharging it under the pressure of said chamber into the outer section of said flue, whereby condensation in the outer section of said flue will be prevented, and the movement of said gases through said flue assisted.

23. The method of preventing condensation in the chimney flue of a furnace which comprises introducinginto said gases while in said flue, a current of a gaseous medium havin such a temperature and humidity and in SIMS} quantity that condensation of moisture in the gasesin said flue will be prevented.

GEORGE G. SCHMIDT. 

